In the field of medicine, there has been active research on drugs that directly and effectively act on the affected area without causing serious side effects. One area of active research is a method known as a drug delivery system (DDS), in which active ingredients of drugs or other substances are specifically delivered to a target cell or tissue, where they can exhibit their effects.
Another area of active research is a technique of gene transfer to a specific cell, which is now essential in the field of molecular cell biology. With the genetic background of various diseases being revealed by the Human Genome Project, a method of highly specific gene transfer to a specific cell or tissue holds great promise because, once the method is established, it is applicable to the field of gene therapy.
In one known example of a gene transfer method to cells, uptake of genes takes place in the form of a giant molecule by endocytosis (calcium phosphate method, lipofectamin method). In another method, genes are transferred through cell membrane pores that are formed by the stimulation of the cell membrane with an electrical pulse (electroporation method, gene gun method). Both of these methods are commonly used in molecular biology experiments.
Despite the simplicity of these methods, they cannot be readily applied to cells or tissues of internal body, because the methods involve direct physical contact with the cells and surgically expose the site of gene transfer. It is also difficult to achieve near 100% uptake.
A transfer method that is safe to use is a liposome method. The liposome method does not damage the cell and is applicable to cells or tissues of internal body. A problem of the method, however, is that the liposome, which is a simple lipid, cannot have a high level of specificity to the cells or tissues, and uptake of genes in vivo is far below the required level.
In a recently developed technique, a therapeutic gene is inserted in viral DNA, and the gene is transferred by an infectious virus. The method is innovative in the sense that it does not expose the site of transfer, is applicable to individuals, and provides near 100% uptake. However, the method suffers from a serious drawback in that the virus non-specifically infects a wide range of cells, transferring the gene to cells other than the target cell. Further, the method has a potential risk of unexpected side effect if the viral genome is incorporated in the chromosomes. In fact, the method is not used in initial stages of disease treatment. Only the terminal patients can receive the benefit of the method.
In sum, none of the conventional gene transfer methods is sufficient to specifically transfer genes to a target cell and express the protein therein to produce a drug. To this date, there has been no effective method of directly delivering a protein as a drug into a target cell or tissue.
Under these circumstances, the inventors of the present invention have previously proposed a method of specifically and safely delivering and transferring various substances (including genes, proteins, compounds) into a target cell or tissue, using hollow nanoparticles of a protein that has the ability to form particles and has incorporated a bio-recognizing molecule, as disclosed in International Publication with International Publication No. WO01/64930 (published on Sep. 7, 2001) (hereinafter referred to as “International Publication WO01/64930”), and in Japanese Publication for Unexamined Publication No. 316298/2001 (published on Nov. 13, 2001). However, these publications do not fully discuss how the method can be used to develop drugs for the treatment of diseased cells or tissues (cancer, for example). Specifically, the development of drugs displaying a specific antibody for specific cancer cells or tissues remains to be one of the most important goals to be achieved, particularly in view of the following problems.
Owning to the difficulty in specifically and safely delivering and transferring a protein (drug) into a target cell or tissue, a great burden has been put on the patients receiving treatment using such a protein drug.
For example, for the treatment of viral hepatitis (hepatitis C in particular), an interferon, which is one form of a protein drug, is administered systemically through intravenous injection over an extended time period. Though the effectiveness of the treatment is well recognized, it has many side effects due to the non-specific action of the interferon, including high fever, loss of hair, tiredness, and immune response, which occur every time the drug is administered.
The hepatocyte growth factor is known to be effective for the treatment of liver cirrhosis. However, since systemic administration of the drug through intravenous injection may cause unexpected side effects, the hepatocyte growth factor is directly administered to the liver with a catheter. The use of catheter requires surgery, which puts a burden on the patient if he or she must receive prolonged treatment.
The present invention was made in view of the foregoing problems, and an object of the invention is to provide a therapeutic drug, proved to be effective by animal testing, that specifically acts on a target cell or tissue with its hollow protein nanoparticles displaying bio-recognizing molecules such as an antibody. The invention also provides a therapeutic method, and hollow nanoparticles for use in such a therapeutic drug and therapeutic method.